Intravascular catheters are presently in wide clinical use for a variety of diagnostic and therapeutic purposes. Intravascular catheterization therapies, such as percutaneous transluminal coronary angioplasty ("PTCA"), have been developed as alternatives to bypass surgery for treating vascular diseases or other conditions that occlude or reduce the lumen size of portions of a patient's vascular system. In particular, balloon angioplasty has proven to be a useful, and in many circumstances preferred, treatment for obstructive coronary diseases.
In a typical PTCA procedure, a guide catheter is introduced into a peripheral artery of a patient, such as a femoral artery through an incision at the groin. The guide catheter is advanced through the femoral or other peripheral artery to a desired coronary site. Typically, the guide catheter is advanced through the aorta until the distal end of the guide catheter is positioned adjacent to the coronary ostium for the coronary artery to be treated. A guide wire is introduced through the guide catheter, and a balloon dilation catheter is then introduced over the guide wire. More particularly, the guide wire is advanced past the distal end of the guide catheter within the lumen of the diseased vessel and manipulated across the region of stenosis. The balloon dilation catheter is then advanced past the distal end of the guide catheter over the guide wire until the balloon is positioned across the region of stenosis. The balloon is then inflated by supplying a fluid under pressure to the balloon through an inflation lumen in the balloon dilation catheter, which stretches the diseased vessel to re-establish acceptable blood flow through the vessel. Intravascular therapeutic and diagnostic procedures utilizing dilation catheters, such as PTCA, have achieved wide acceptance because of their effectiveness and because they involve a relatively minor surgical procedure as compared to coronary bypass surgery.
Advancing a catheter to position a balloon across a stenotic lesion can be a difficult and time consuming task due to the tortuous passages through which the catheter must be navigated by a physician. The efficacy of such procedures relies upon the balloon being precisely positioned at the desired location. Furthermore, catheters must be able to traverse tortuous pathways in a patient's vasculature in a manner as atraumatic to the patient as possible. To satisfy these requirements, catheters must balance a number of competing design criteria. Specifically, catheters should have a small profile to permit navigation through small body lumens. The catheter must be axially strong along its longitudinal length to give the catheter "pushability" for transmitting a longitudinal force along the catheter so a physician can push the catheter through the vascular system to the stenosis. At the same time, however, the catheter must be flexible so that the catheter has good "trackability" so as to be able to navigate the tortuous passages of a patient's vascular system.
To satisfy these competing design criteria, catheters typically have a stiff proximal portion and a flexible distal portion to which the inflation balloon is attached. The stiff proximal portion gives the catheter sufficient axial and longitudinal strength to give the catheter pushability, while the flexible distal portion permits the catheter to pass through tortuous, tight curvatures of the vasculature.
One type of balloon dilation catheter, commonly referred to as an "over-the-wire" catheter, typically includes a single lumen shaft that extends from the proximal end of the catheter to the distal end of the balloon. A guide wire is inserted into and extends along the length of the single lumen shaft. The guide wire is used to steer the catheter through the patient's vasculature by advancing the catheter over the previously inserted wire until the balloon is positioned at a desired treatment location. In this catheter, the guide wire must be inserted into and through the entire length of the dilation catheter prior to the catheter being inserted into a patient's vasculature. As such, the guide wire must protrude from the patient's body by a length greater than the length of the dilation catheter. Moreover, because the guide wire extends through the length of the catheter there is relatively large friction between the guide wire and the catheter. As a result, manipulation of an over-the-wire dilation catheter can be difficult.
A catheter design that alleviates these shortcomings is referred to as a "rapid-exchange" catheter. An example of a rapid-exchange catheter is described in United States Patent Reexamination Certificate B1 4,762,129 to Bonzel, the entire disclosure of which is hereby incorporated by reference for all purposes.
While catheters of the rapid-exchange type have been highly successful in PTCA procedures, the flexible distal portion of such catheters may kink and/or buckle when the catheter is subjected to high axial loads. A region of the catheter where such kinking and buckling can occur is the interface between the stiff proximal portion and the flexible distal portion of the catheter due to the change in stiffness at this interface. Attempts have been made to provide a structure that resists kinking and buckling in this region. Such structures are described in U.S. Pat. No. 5,156,594 to Keith, U.S. Pat. No. 5,658,251 to Ressemann et al, and U.S. Pat. No. 4,748,982 to Horzewski et al.
There is a continuing need for improved catheters, however. In particular, a rapid-exchange catheter having a stiffening member that provides a gradually varying stiffness at the interface between a stiff proximal portion and a flexible distal portion of the catheter is highly desirable. Such a stiffening member should be efficient to manufacture and use, and should be effective in providing sufficient stiffness to the interface between the proximal and distal portions of the catheter, while not unduly influencing the flexibility of the catheter.